Airfield: Nazi zombie building
Go to the multiplayer map "Airfield". Go to the first side, which is the one where you spawn behind the big building then go out to the field. Instead, go inside the building and examine it. Look around at the pillars and windows, then go upstairs to the left. Look around some more and on the balcony. Notice it is the same building in the Nacht Der Untoten (zombie) mission, except all the entrances are walled up or blocked by an invisible wall.

Little Resistance: Ray gun
After the boat crashes, call in an air strike on the specified location. Run up to the beach and move to the right. You will find a small puddle at the right side of the beach. Stand in it briefly, then move towards the middle of the beach to find a smaller puddle. Stand in that puddle briefly. Move towards the far left side of the beach. Stand briefly in the puddle in the barb wire. After several seconds the screen will shake and you will hear strange voices. Four lion statues will rise out of the ground with alien ray guns in their mouths.

Getting more ammunition
Use the following trick if run out or are running low on ammunition on any mission in Solo mode. Find a non-essential teammate (someone not involved in the story line). Walk up to him and aim the reticule next to his head or torso. Knife the air, and as you do so move slightly towards them so that the reticule is over them. If done correctly, your teammate should die and should drop his weapon. The difficulty setting will not matter. Non-essential teammates will get replaced when you walk into a battle. If the teammate does not die but keeps getting back up, they are essential to the story (for example, Sgt Roebuck and Sgt Rezenov).

Easy "Rough Economy" trophy
Play the Vendetta mission. After you shoot Amsel's guards and move up to the car with the sergeant, a group of Nazis will appear down the street. Do not follow the sergeant. Instead, stay near the car and wait for three of the Nazis to get in a line, then shoot.

Trophies
Complete the following tasks to unlock PlayStation3 trophy rewards.

Get Your Hands Dirty (Bronze): Complete 'Semper Fi' on Veteran difficulty. (Solo only).
Bloody Peleliu (Bronze): Complete 'Little Resistance' on Veteran difficulty. (Solo only).
The Sword Is Broken (Bronze): Complete 'Hard Landing' on Veteran difficulty. (Solo only).
Architect (Bronze): Complete 'Vendetta' on Veteran difficulty. (Solo only).
The Hammer Strikes (Bronze): Complete 'Their Land, Their Blood' on Veteran difficulty. (Solo only).
Scorched Earth (Bronze): Complete 'Burn 'em Out' on Veteran difficulty. (Solo only).
Fearless (Bronze): Complete 'Relentless' on Veteran difficulty. (Solo only).
Hell on Wheels (Bronze): Complete 'Blood and Iron' on Veteran difficulty. (Solo only).
No Return (Bronze): Complete 'Ring of Steel' on Veteran difficulty. (Solo only).
One Bad Gato (Bronze): Complete 'Eviction' on Veteran difficulty. (Solo only).
Blowtorch and Corkscrew (Bronze): Complete 'Blackcats' on Veteran difficulty. (Solo only).
The Sun Sets (Bronze): Complete 'Blowtorch and Corkscrew' on Veteran difficulty. (Solo only).
For the Motherland (Bronze): Complete 'Breaking Point' on Veteran difficulty. (Solo only).
Bearing the Burden (Bronze): Complete 'Heart of the Reich' on Veteran difficulty. (Solo only).
Carlson's Raiders (Bronze): Complete 'Downfall' on Veteran difficulty. (Solo only).
Weapon of Mass Destruction (Bronze): Save the soldier before he burns to death.
The Professional (Bronze): Radio in a naval bombardment that kills at least 4 Japanese soldiers.
Rough Economy (Bronze): In 'Black Cats', blast out all of the spot lights in the Japanese cargo convoy. (Solo only).
Guardian Angel (Bronze): Kill 3 enemies with a single round.
Close Shave (Bronze): In the final battle for Okinawa, save Sergeant Roebuck.
Snake in the Grass (Bronze): Survive a banzai attack. (Solo only).
Grave Robber (Bronze): Take out a Japanese soldier lying in wait in the grass.
Throw a Six and a Half (Bronze): Burn an enemy out of a tree with the flamethrower in 'Hard Landing'.
Firestarter (Bronze): When staring into the face of adversity, show courage and persevere.
Mortar-dom (Bronze): Kill 15 enemies while mounted on a tank in 'Ring of Steel'.
Shot in the Dark (Bronze): Kill 8 Japanese with thrown mortars in 'Breaking Point.
Sum of All Zeros (Bronze): Kill 10 enemies while the lights are out in the subway in 'Eviction'.
Get Your Left Foot Wet (Bronze): Complete a 4-player Competitive Co-Op match in 1st place. (Online co-op Only).
Get Your Right Foot Wet (Bronze): Complete a match in Campaign Co-Op mode. (Online co-op only).
(Bronze): Complete a match in Competitive Co-Op mode. (Online co-op only).
Stormed Peleliu (Silver): Complete 'Semper Fi' on any difficulty. (Solo only).
The Last Stand (Silver): Establish a beachhead at Peleliu Island on any difficulty. (Solo only).
Stabbed in the Heart (Silver): Survive the conflict in Okinawa on any difficulty. (Solo only).
Hardened War Hero (Silver): Complete all missions on the Eastern Front on any difficulty. (Solo only).
Gunslinger (Silver): Shoot all of Amsel's henchmen, including their attack dog, without reloading. (Solo only).
Lights Out! (Silver): Assassinate General Amsel with a pistol shot. (Solo only).
No Safe Place (Silver): Collect all Death Cards in the game. (Solo only).
Purple Heart (Silver): On Hardened or Veteran difficulty, complete a level without dying. (Solo only).
Kamikaze (Silver): Complete a level using only the flamethrower. Melee, grenades & explosives are OK.
Iron Fist (Silver): Complete a level on Regular difficulty or higher using only melee or grenades. (Solo only).
Ruthless (Silver): Destroy all towers and bunkers in 'Blood and Iron'.
Blue Ribbon (Silver): Down 45 Japanese Zeros in 'Black Cats'. (Solo only).
War Hero (Gold): Complete the game on Hardened or Veteran difficulty. (Solo only).
Saved Private Ryan (Gold): Save the soldier before he burns to death. (Solo or co-op).
Platinum (Platinum): Awarded when all other trophies have been unlocked.